In recent years, there have been proposed and developed various hydraulically-operated vane member equipped variable valve timing control devices, capable of locking a vane member at an intermediate position between a maximum phase-advance position and a maximum phase-retard position by means of a lock mechanism. One such variable valve timing control device has been disclosed in Japanese Patent Provisional Publication No. 2010-537120 (hereinafter is referred to as “JP2010-537120”), corresponding to U.S. Pat. No. 7,874,274, issued on Jan. 25, 2011. In the valve timing control device disclosed in JP2010-537120, a large-diameter rotor is rotatably accommodated in a housing, and radially-outward spring-loaded five vanes are installed in respective vane grooves in the outer periphery of the rotor. Also provided is a lock mechanism arranged between the rotor and a front plate (a first side cover). The lock mechanism is comprised of two slidable lock pins held in respective accommodation bores of the rotor, and two lock holes (two lock-pin receptacles) formed in the front plate so as to permit sliding movement of the lock pin into and out of engagement with the associated lock hole.
As discussed above, in the valve timing control device disclosed in JP2010-537120, the lock pins are installed on the rotor rather than the respective vanes. This contributes to a reduction in circumferential thickness of each of the vanes, thereby enlarging a relative-rotation angle of a camshaft (the rotor) relative to an engine crankshaft (the housing with a chain wheel or a timing sprocket).